Big-city heat has big effect, study says

Monday

Jan 28, 2013 at 12:01 AMJan 28, 2013 at 11:58 AM

WASHINGTON - The energy big cities burn - mostly coal and oil to produce power - also produces excess heat that can get into atmospheric currents and influence temperatures thousands of miles away, a new study found.

WASHINGTON — The energy big cities burn — mostly coal and oil to produce power — also produces excess heat that can get into atmospheric currents and influence temperatures thousands of miles away, a new study found.

The so-called waste heat that leaks out of buildings, vehicles and other sources in major Northern Hemisphere cities makes winters warmer across huge swaths of northern Asia and northern North America, according to a report published yesterday in the journal Nature Climate Change.

That is different from what has long been known as the urban-heat island effect, where city buildings, roads and sidewalks hold on to the day’s warmth and make the urban area hotter than the surrounding countryside.

Instead, the researchers wrote, the excess heat given off by burning fossil fuels appears to change air-circulation patterns and then hitch a ride on air and ocean currents, including the jet stream.

Study author Aixue Hu of the National Center for Atmospheric Research in Colorado said in a statement that the excess heat generated by this burning in cities could change atmospheric patterns to raise or lower temperatures far afield.

Some remote locations heat up by as much as 1.8 degrees Fahrenheit as a result, the study said. But some parts of Europe cool off a bit because of the way urban waste heat changes atmospheric circulation.

The impact on global mean temperature is negligible, because the total amount of waste heat from human activities is about one-third of 1 percent of the total amount of heat carried across high latitudes by air currents and oceans.

But this waste heat from cities and the way it moves around could help explain why some places are warmer in winter than climate computer models predict, the researchers said.